It is known to replace diseased or damaged articulating surfaces of an ankle joint with prosthetic components. For example, the prosthesis may comprise a tibial component implanted into the tibia of the patient and a talar component implanted into the talus of the patient. In addition, a bearing insert may be provided between the tibial and talar components.
The insert may be fixed with respect to the tibial component. Such a fixed insert may comprise an articulating surface for engagement with a corresponding articulating surface on the talar component. Alternatively, the insert may be free to move with respect to the tibial component. Such an unconstrained insert may comprise two articulating surfaces, one for engaging each of the tibial and talar components. As a result, the unconstrained insert may provide improved articulation thanks to the additional degrees of freedom.
However, there is a risk that unconstrained mobile bearing inserts may become dislodged during use and for this reason such unconstrained inserts are presently not permitted by one or more regulation authorities, at least not without a lengthy approval process. Furthermore, a fixed insert requires accurate placement during surgery as the insert is not free to move once installed. The accurate placement required is difficult and time consuming to achieve and costly to subsequently correct.
There is also the issue of the limited access available to a surgeon when performing an ankle replacement operation. Unlike the knee, which thanks to its greater range of articulation is able to expose a greater working area for the surgeon, the ankle presents a smaller access area to the surgeon. The present invention also seeks to address this issue.